Treatment of cellulose-containing fabrics with cellulase is carried out to provide the fabrics with desired properties. For example, treatment with cellulase is carried out in the fabric industry in order to improve the feel and appearance of cellulose-containing fabrics or to give colored cellulose-containing fabrics an appearance of “stone-washed” material, i.e., partial color change (European Patent No. 307,564).
Colored cellulose-containing fabrics are known to become fuzzy after repeated washings and to lose their vividness. Incorporation of cellulase into a detergent can remove fuzz and make the color of fabrics vivid, i.e., clarify the color (European Patent No. 220,016). Thus, detergents containing cellulase are commercially available mainly in Europe and America.
In the aforementioned application, cellulases derived from Trichoderma or Humicola (both are wood-rotting fungi) are mainly used. Recently used cellulase preparations are produced by isolating endoglucanases, which are highly active in fabric treatment, from these cellulase components and enhancing their effects with genetic engineering in order to improve commercial efficiency. Examples of these highly active endoglucanases include: Humicola insolens-derived EG V (WO 91/17243) and NCE4 (WO 98/03640) that strongly act on cotton fabrics; and Rhizopus oryzae-derived RCE I, RCE II, and RCE III, Mucor circinelloides-derived MCE I and MCE II, and Phycomyces nitens-derived PCE I (WO 00/24879) that strongly act on lyocell fabrics.
Among endoglucanases used in the aforementioned applications, EG V (WO 91/17243), NCE4 (WO 98/03640), and RCE I, RCE II, RCE III, MCE I, MCE II, and PCE I (WO 00/24879) are presumed to belong to the same family (family 45) because of their amino acid sequences, and these enzymes have common structural properties. Specifically, each of these endoglucanases comprises a cellulose-binding domain for binding to cellulose as its substrate (hereinafter referred to as “CBD”), a catalytic active domain as an active center (hereinafter referred to as “CAD”), and a linker domain with a high hydrophilic amino acid residue content for linking these two domains.
EG V, an endoglucanase belonging to family 45, was studied using an enzyme, the CBD domain of which had been deleted (JP Patent Publication (PCT Translation) No. 9-500667, Enzyme and Microbial Technology, 27 (2000), 325-329). However, no improvement has been reported regarding the activity of endoglucanase for removing fuzz from cellulose fabrics through the deletion of the cellulose-binding domain (CBD). There are still many unclarified matters concerning the role of the cellulose-binding domain of endoglucanase in the exhibition of endoglucanase activity, and research thereof is limited to cellulase derived from a specific fungus, namely, Trichoderma (Kiovula, A. et al., Trichoderma Gliocladium, 2, (1998), 3-23). There has been no detailed research on the cellulose-binding domain of the Zygomycetes-derived endoglucanase.
Up to the present, several contrivances have been made in order to improve the effect or performance of cellulase in the above applications. For example, mutation was applied to an enzyme for improvement thereof, or culture conditions were modified in order to improve the productivity of the enzyme. Due to the high cost of cellulase to be used, however, the effect of cellulase should be further improved in order to provide a cellulase preparation that is worth using at an industrially practical level. Recently used cellulase preparations are produced by reinforcing only endoglucanase, which is highly active in fabric treatment, with genetic engineering in order to improve commercial efficiency. Accordingly, it is desirable to further improve the activity of such highly active cellulase.